Good Sources of Energy
Energy comes in different forms and one form can be converted to another. Energy, in the usable form, is dissipated to the surroundings in less usable forms. Hence, any source of energy we use, to do work, is consumed and cannot be used again.
Characteristics of Good Fuel
- It should have a high calorific value, i.e., it should release a large amount of heat on burning.
- It should not produce a lot of smoke.
- It should be readily available.
Characteristics of a Source of Energy
- It should do a large amount of work per unit volume or mass.
- It must be convenient to use.
- It should be easy to transport and store.
- It should be capable of delivering a desired quantity of energy at a steady rate over a long period of time.
- Be economical
Example 1.
Case-Based:
List four forms of energy that you use from the morning, when you wake up, till you reach school. Identify the sources of these different forms of energy.
Let us find out the various options we have when we choose a fuel for cooking our food and the criteria one would consider when trying to categorize something like a good fuel.
(A) The different forms of energy that we use in our daily life in urban homes are:
Select the row containing the incorrect option:
| Form of energy | Source |
| (a) Electrical energy | Water or coal |
| (b) Muscular energy | Food |
| (c) Heat energy | Fossil fuels |
| (d) Mechanical energy | Wood |
Answer:
(d) Form of Energy: Mechanical energy; Source: Wood
Explanation: Mechanical energy is used in our daily life in cycling, mixer etc. The source may be electrical or chemical energy, but not wood, as wood is not considered a good source of energy.
(B) Given below are statements regarding choosing a fuel for cooking our food. Select the incorrect statements.
(I) Kerosene should be used as a cooking fuel as it is readily available.
(II) LPG or Natural Gas should not be used for cooking as they emit a lot of smoke.
(III) Biogas should be used as a cooking fuel in rural areas since it is a renewable source of energy.
(IV) Coal should not be used as a cooking fuel since it is produces a lot of smoke on burning.
(a) Both (I) and (II)
(b) Both (II) and (III)
(c) Both (III) and (IV)
(d) Both (I) and (IV)
Answer:
(a) Both (I) and (II)
Explanation: Though kerosene is readily avail-able, it should not be used as a cooking fuel as it emits harmful pollutants. Liquefied Petroleum Gas (LPG) or Natural Gas should be used for cooking as they do not emit any smoke when burnt.
(C) Write two criteria one would consider when trying to categorise something as a good fuel.
Answer:
- Amount of heat produced on burning fuel
- Ease of availability
(D) How would the choice of fuel for cooking be different if you lived in a forest and in New Delhi?
Answer:
Some of the factors deciding the choice of fuel are the ease of availability, transportation, storage and cost. If a person lived in a forest, he would mainly use firewood as fuel, since it is readily available. However, for a person living in a city like New Delhi, he would use LPG or Natural gas (piped natural gas) as a fuel for cooking since it is readily available and produces no smoke.
(E) Assertion (A): Different fuels are used for cooking and heating room in winter.
Reason (R): Calorific value of fuels is the only criteria for selecting a fuel.
(a) Both (A) and (R) are true and (R) is the correct explanation of the assertion.
(b) Both (A) and (R) are true, but (R) is not the correct explanation of the assertion.
(c) (A) is true, but (R) is false.
(d) (A) is false, but (R) is true.
Answer:
(c) (A) is true, but (R) is false.
Explanation: The choice of fuels depends on several factors such as calorific value of fuels, availability, cost, ease of storage and transport, emission of smoke etc.
Example 2.
If you could use any source of energy for heating your food, which one would you use and why?
Answer:
Fuel that heats the food faster without destroying the nutritional value of the food would be preferred for heating food. So, an electric oven or a heater would be better.